or taking other medicines with guanfacine, like tenex. intuniv may cause serious side effects, such as low blood pressure, low heart rate, fainting, and sleepiness. intuniv may affect the ability to drive or use machinery. other side effects include nausea, tiredness, trouble sleeping, stomach pain, and dizziness. tell the doctor about your child's medicines and medical conditions, including heart, liver, or kidney problems. [ woman ] adding intuniv helped eric. [ male announcer ] ask the doctor about once-daily nonstimulant intuniv.